Falling Objects – Balanced and Unbalanced forces (35 mins)
Q1.On 14 October 2012, a skydiver set a world record for the highest free fall from an aircraft.
After falling from the aircraft, he reached a maximum steady velocity of 373 m / s after 632
seconds.
(a)
Draw a ring around the correct answer to complete the sentence.
frictional
This maximum steady velocity is called the
initial
velocity.
terminal
(1)
(b)
The skydiver wore a chest pack containing monitoring and tracking equipment.
The weight of the chest pack was 54 N.
The gravitational field strength is 10 N / kg.
Calculate the mass of the chest pack.
Use the correct equation from Section A of the Physics Equations Sheet.
.........................................................................................................................
.........................................................................................................................
Mass of chest pack = ........................................ kg
(2)
(c)
During his fall, the skydiver’s acceleration was not uniform.
Immediately after leaving the aircraft, the skydiver’s acceleration was 10 m / s2.
(i)
Without any calculation, estimate his acceleration a few seconds after leaving
the aircraft.
Explain your value of acceleration in terms of forces.
Estimate ................................................................................................
Explanation ............................................................................................
................................................................................................................
................................................................................................................
................................................................................................................
................................................................................................................
(3)
Page 1
(ii)
Without any calculation, estimate his acceleration 632 seconds after leaving
the aircraft.
Explain your value of acceleration in terms of forces.
Estimate ................................................................................................
Explanation ............................................................................................
................................................................................................................
................................................................................................................
................................................................................................................
................................................................................................................
................................................................................................................
(3)
(Total 9 marks)
Q2.
A small object falls out of a balloon.
Choose words from the list to complete the sentences below.
friction
gravity
air pressure
accelerates
falls at a steady speed
slows down
•
The weight of an object is the force of ............................................ which acts on it.
•
When you drop something, first of all it ............................................... .
•
The faster it falls, the bigger the force of ........................................... which acts on it.
•
Eventually the object ............................................. .
(Total 4 marks)
Page 2
Q3.
A sky-diver jumps from a plane.
The sky-diver is shown in the diagram below.
(a)
Arrows X and Y show two forces acting on the sky-diver as he falls.
(i)
Name the forces X and Y.
X ..........................................................
Y ..........................................................
(2)
(ii)
Explain why force X acts in an upward direction.
...........................................................................................................................
...........................................................................................................................
(1)
(iii)
At first forces X and Y are unbalanced.
Which of the forces will be bigger? .......................................
(1)
(iv)
How does this unbalanced force affect the sky-diver?
...........................................................................................................................
...........................................................................................................................
(2)
Page 3
(b)
After some time the sky-diver pulls the rip cord and the parachute opens.
The sky-diver and parachute are shown in the diagram below.
After a while forces X and Y are balanced.
Underline the correct answer in each line below.
Force X has
increased / stayed the same / decreased.
Force Y has
increased / stayed the same / decreased.
The speed of the sky-diver will
increase / stay the same / decrease.
(3)
Page 4
(c)
The graph below shows how the height of the sky-diver changes with time.
(i)
Which part of the graph, AB, BC or CD shows the sky-diver falling at a
constant speed?
................................................
(1)
(ii)
What distance does the sky-diver fall at a constant speed?
Distance .............................. m
(1)
(iii)
How long does he fall at this speed?
Time .................................... s
(1)
(iv)
Calculate this speed.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
Speed .............................. m/s
(2)
(Total 14 marks)
Q4.
(a)
The diagram shows a steel ball-bearing falling through a tube of oil.
Page 5
The forces, L and M, act on the ball-bearing.
What causes force L? ......................................................................... (1)
(b)
The distance – time graph represents the motion of the ball-bearing as it falls through the oil.
(i)
Explain, in terms of the forces, L and M, why the ball-bearing accelerates at
first but then falls at constant speed.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(3)
(ii)
What name is given to the constant speed reached by the falling ball-bearing?
...........................................................................................................................
(1)
(iii)
Calculate the constant speed reached by the ball-bearing.
Show clearly how you use the graph to work out your answer.
...........................................................................................................................
...........................................................................................................................
Speed = ............................................................ m/s
(2)
(Total 7 marks)
Page 6
Mark Scheme – Falling Objects: Balanced and Unbalanced forces
M1.(a)
terminal
1
(b)
5.4 (kg)
correct substitution of 54 = m × 10 gains 1 mark
2
(c)
(i)
0< a <10
1
some upward force
accept some drag / air resistance
1
reduced resultant force
1
(ii)
0
1
upward force = weight (gravity)
1
resultant force zero
1
[9]
•
M2.
gravity
•
accelerates
•
friction
•
falls at a steady speed
each for 1 mark
Page 7
[4]
M3.
(a)
(i)
air resistance/drag/friction (or upthrust)
weight/gravitational pull/gravity
for 1 mark each
1
(ii)
air resistance/friction acts in opposite direction to motion
1
(iii)
Y
1
(iv)
the sky-diver accelerates/his speed increases
in downward direction/towards the Earth/falls
for 1 mark each
2
(b)
force X has increased force Y has stayed the same the speed of the sky-diver
will stay the same
for 1 mark each
3
(c)
(i)
CD
1
3
(iv)
10 (but apply e.c.f. from (ii) and (iii))
gets 2 marks
or 500/50 or d/t
gets 1 mark
2
[14]
M4.
(a)
gravity
Page 8
accept weight
do not accept mass
accept gravitational pull
1
(b)
(i)
Initially force L greater than force M
accept there is a resultant force downwards
1
(as speed increases) force M increases
accept the resultant force decreases
1
when M = L, (speed is constant)
accept resultant force is 0
accept gravity/weighty for L
accept drag/ upthrust/resistance/friction for M
do not accept air resistance for M but penalise only once
1
(ii)
terminal velocity
1
(iii)
0.15
accept an answer between 0.14 – 0.16
an answer of 0.1 gains no credit
allow 1 mark for showing correct use of the graph
2
[7]
Page 9